The invention described herein relates to the field of flow meters, and more particularly to flow meters used in industrial paint spraying apparatus. More particularly, it relates to a method and apparatus for communicating two channels of flow meter information from the spray head along a single optical fiber cable from the metering apparatus mounted on the spray head to a unit located remote from the spray head, which may then provide two channels of output for interfacing with a system controller for controlling the industrial spraying apparatus.
In industrial spraying apparatus, it is desirous to have sensors mounted in the spray head as opposed to elsewhere in the dispensing circuit, in order to accurately measure the rate of flow of the fluid being dispensed from the spray head.
The known industrial painting systems use electrostatic means to charge the paint to reduce waste and improve coverage during the painting operation. The historical use of solvent based paints, which are non-conductive, allowed the use of a conventional wired transmitter on the flow meter in the spray head. Due to environmental and other concerns, the paint industry is moving toward the use of water based paints, which are inherently conductive. With water based paints the flow meter can no longer be grounded as in the prior art spray apparatus, as this would short-circuit the electrostatic charging voltage. The use of a fiber-optic interface between the flow meter and the other electronics of the dispensing system allows the meter to be electrically xe2x80x9cfloatedxe2x80x9d while the fiber optic cable isolates the receiver and control electronics from any voltage that may be present on the flow meter due to its location on the spray head. This system although initially designed for industrial spray painting systems could have other applications where dielectric isolation of the spray head and meter and intrinsic safety are important.
Presently, there are two systems on the market that use a fiber optic cable to transmit flow rate information from a flow meter on a spray head to a system controller. Among other differences, neither system allows for transmission of quadrature signals or two channels of information on one fiber optic channel and neither provides flow direction information, which allows for detection of a leaking or malfunctioning valve in the industrial spraying system.
Broady described, the invention herein is a method and apparatus for sensing the rate and direction of a moving body by generating two signals, converting rate and direction information into a single signal capable of being transmitted along a single communications channel, and reconstructing said rate and direction information after transmission.
In the particular application described in the preferred embodiment, the invention described herein is a method and apparatus for transmitting flow rate and direction information from a flow meter to a system controller by converting analog signals into a digital signal transmitted by pulses of light through a single optical fiber to a receiver, where the information is regenerated into conventional two channel quadrature signals suitable for input into a system controller. The apparatus, having both a transmitter section and a receiver section, may be referred to as a transceiver. The apparatus is specifically designed for industrial spray painting systems, but may be applied to other applications.
In general, the spraying apparatus employs a spray head integrating a flow meter or with a flow meter attached thereto. The flow meter includes at least two sensors that generate quadrature signals which are fed to a transmitter for transmission along a single communication channel to a receiver unit which receives and processes the signal for use by a system controller that controls the amount of fluid sprayed from the spray head. The flow meter is associated with a transmitter to encode the signals received from the sensors into light pulses. The communication channel used herein is a fiber optic cable which transmits the light pulses to the receiving unit which then converts the digital light pulses into electromagnetic signals usable by the controller electronics. The pulses of light encode the quadrature signals from the sensors so that the light pulse frequency represents the rotation rate of the gears as sensed by the sensors, and the pulse width represents the direction of rotation of the meter gears or flow through the meter.